The use of "dipsticks" in assaying for the presence of an analyte in a sample is known in the art. Typical analytes comprise such materials as drugs, nucleic acids, proteins, pollutants, fine chemicals, such as, physiological compounds, and the like. In a typical dipstick based analytical assay, a ligand, which specifically binds to the analyte of interest, is bound to a solid support on the dipstick. The dipstick is contacted with a sample in which the presence of the analyte of interest is to be determined. Frequently, steps are employed to aid in the removal of non-specifically bound material from the dipstick. Finally, the dipstick is processed to determine the presence of the analyte. The dipstick generally comprises a solid material, which is planar or columnar in geometry. U.S. Pat. No. 4,391,904 to Litman et al. (incorporated herein by reference) describes test strip kits wherein a member of an immunological pair is bonded to a solid surface. Herzberg et al., U.S. Pat. No. Des. 293,374, disclose an assay card with tapered ends.
In one widespread format, the dipstick is transferred through one or more liquid reagent filled analytical wells. In this format, complete immersion of the solid support requires filling the analytical well with liquid reagent to a depth which approximates the distance between the solid support and the distal end of the dipstick. While this format provides a convenient means of assaying for an analyte, the cost of the liquid reagent may dramatically increase the cost of the assay and increasing the volume of the reagent by dilution decreases the inherent sensitivity of the assay. Mixing of the liquid by reciprocating the dipstick in and out of the solution is frequently used to hasten processing. However, the configuration of prior art dipsticks is not optimized to perform this function. Further, upon removal from the reagent, droplets suspended from the dipstick may contaminate subsequent processing steps necessitating longer or additional processing.
In developing an assay, it is desirable to minimize the number of processing steps, the time between steps, and the reagent volume employed at each step, while simultaneously maximizing the sensitivity of the assay. While effort has been made to optimize reagent chemistry to achieve these ends, the analytical dipstick configuration has changed little. It is therefore desirable to develop a novel dipstick configuration for improving assay performance.